Recently, for the reasons of the strength, the ability to protect products and the working environment aptitude as wrapping materials and of the advertising effect by printing thereon, complex flexible films containing a combination of different types of polymer materials have become the mainstream in the art. Such complex films generally have a thermoplastic film layer to be the outer layer that plays a role of product protection, and a thermoplastic film layer to be a sealant layer; and for sticking these, there is employed a dry lamination method of applying an adhesive to a laminate film layer followed by adhering a sealant layer thereto, or an extrusion lamination method of optionally applying an anchor coating agent to a laminate film layer followed by melting and applying a plastic film to be a sealant layer thereto under pressure for film-like lamination.
The mainstream of the adhesive to be used in these methods is, in general, a two-pack polyurethane adhesive that contains a main ingredient having an active hydrogen group such as a hydroxyl group or the like and a curing agent having an isocyanate group, from the viewpoint of the high adhesive performance thereof (see Patent References 1 and 2).
However, in general, the curing reaction of the two-pack polyurethane adhesive of the type is not so rapid, and therefore the adhesive requires curing promotion by aging for a long period of time of from 1 to 5 days after sticking therewith, for securing sufficient adhesion. In addition, the adhesive uses a curing agent having an isocyanate group, and therefore in case where the unreacted isocyanate group remains after curing, the remaining isocyanate group would react with moisture in air to generate carbon dioxide, therefore bringing about a problem in that bubbles may form inside the laminate film.
On the other hand, as a method for solving the problem, there are proposed a polyurethane adhesive and an epoxy adhesive for lamination (see Patent References 3 and 4).
However, the gas barrier property of the polyurethane adhesive and the epoxy adhesive for lamination mentioned above is not good, and therefore, in use thereof for wrapping materials that require gas barrier performance, a layer capable of playing a role of adhesion such as an adhesive layer, an anchor coat layer or the like must be additionally laminated between a gas barrier layer such as a PVDC coat layer, a polyvinyl alcohol (PVA) coat layer, an ethylene-vinyl alcohol copolymer (EVOH) film layer, a polymetaxylylenadipamide film layer, an inorganic substance deposited film layer with alumina, silica or the like deposited thereon or the like, and a flexible polymer film layer to be a sealant layer (see Patent Reference 5), which is, however, disadvantageous in that the laminate film production cost would increase and the lamination working process would be complicated.
As a method for solving the problem, there is proposed an adhesive for gas-barrier lamination (see patent Reference 6). However, though the proposed epoxy resin composition could exhibit a good gas barrier property, it is a two-pack adhesive, and therefore, its pot life is short. Accordingly, a one-pack gas-barrier adhesive coating material having good workability is desired.